Pathogenesis of pneumococcal infection involves a series of interactions between virulence factors and the host defense mechanisms. Pneumococcal virulence factors include capsular polysaccharide (PS), pneumolysin (ply),and autolysin. Pneumolysin has a molecular weight of 53,000 with 471 amino acid residues. Autolysin amidase has a molecular weight of 36,000. The autolytic enzyme isolated from pathogenic type 19F enhanced the release of pneumolysin activity in a pneumococcal type 1 strain. Young mice from mothers injected with type 19F PS-ply conjugate during gestation that received an additional dose of the conjugate after birth, produced higher 19F PS antibody response in young mice, more rapid bacterial clearance from blood and conferred protective immunity. These results suggest that the development of a PS-protein conjugate vaccine for selected pneumococcal types will help in solving problems of low immunogenicity of PS antigens in young children.